MIC2199 MICREL [Micrel Semiconductor], MIC2199 Datasheet - Page 6

• Manufacturer Part Number: MIC2199
• Manufacturer: MICREL [Micrel Semiconductor]

MIC2199
Block Diagram
Functional Description
The MIC2199 is a BiCMOS, switched-mode, synchronous
step-down (buck) converter controller. Current-mode control
is used to achieve superior transient line and load regulation.
An internal corrective ramp provides slope compensation for
stable operation above a 50% duty cycle. The controller is
optimized for high-efficiency, high-performance DC-DC con-
verter applications.
The MIC2199 block diagram is shown above.
The MIC2199 controller is divided into 5 functions.
MIC2199
• Control loop
• Current limit
• Reference, enable and UVLO
• MOSFET gate drive
• Oscillator
C
R
COMP
COMP
EN/UVLO
COMP
2
1
MIC2199
RESET
Oscillator
PWM
Control
Logic
CORRECTIVE
RAMP
Current
Limit
100k
Error
Amp
Figure 1. Internal Block Diagram
Reference
G
m
= 0.2×10
Current
Sense
Amp
6
V
-3
V
A
DD
IN
V
Control Loop
The MIC2199 operates in PWM (pulse-width-modulation)
mode. In PWM mode, the synchronous buck converter forces
continuous current to flow in the inductor which also improves
cross regulation of transformer coupled, multiple output con-
figurations.
PWM Control Loop
The MIC2199 uses current-mode control to regulate the
output voltage. This method senses the output voltage (outer
loop) and the inductor current (inner loop). It uses inductor
current and output voltage to determine the duty cycle of the
buck converter. Sampling the inductor current removes the
inductor from the control loop, which simplifies compensa-
tion.
A block diagram of the MIC2199 PWM current-mode control
loop is shown in Figure 2 and the PWM mode voltage and
current waveform is shown in Figure 3. The inductor current
is sensed by measuring the voltage across the resistor, R
= 2
VDD
7
VIN
6
BST
10
HSD
12
VSW
11
LSD
8
PGND
9
CSH
4
VOUT
5
FB
3
V
IN
Q2
Q1
V
V
OUT
OUT(max)
=
C
D2
C
D1
0.8V
IN
BST
= .0
L1
6 V
⎛
⎝
1
+
R1
R2
⎞
⎠
4.7µF
R
CS
November 2004
R1
R2
V
C
OUT
OUT
Micrel
CS
.